Matthew 23:27

Wo to you, scribes and Pharisees, hypocrites; for ye are like whited sepulchres, which outwardly indeed appear beautiful, but within are full of dead men's bones and of all uncleanness.

Luke 11:44

and salutations in the markets. Wo to you; for ye are as graves which appear not, and men that walk over them are not aware.

Treasury of Scripture Knowledge

Summary

And whosoever toucheth one that is slain with a sword in the open fields, or a dead body, or a bone of a man, or a grave, shall be unclean seven days.

Bible References

A grave

Matthew 23:27
Wo to you, scribes and Pharisees, hypocrites; for ye are like whited sepulchres, which outwardly indeed appear beautiful, but within are full of dead men's bones and of all uncleanness.
Luke 11:44
and salutations in the markets. Wo to you; for ye are as graves which appear not, and men that walk over them are not aware.